To prevent preeclampsia, the WHO recommends antenatal calcium supplementation in populations with inadequate habitual intake. The WHO recommends 1500-2000 mg Ca/d with iron-folic acid (IFA) taken separately, a complex pill-taking regimen. The objective of this study was to test the hypothesis that simpler regimens with lower daily dosages would lead to higher adherence and similar supplement intake. In the Micronutrient Initiative Calcium Supplementation study, we compared the mean daily supplement intake associated with 2 dosing regimens with the use of a parallel, cluster-randomized noninferiority trial implemented in 16 primary health care facilities in rural Kenya. The standard regimen was 3 × 500 mg Ca/d in 3 pill-taking events, and the low-dose regimen was 2 × 500 mg Ca/d in 2 pill-taking events; both regimens included a 200 IU cholecalciferol and calcium pill and a separate IFA pill. We enrolled 990 pregnant women between 16 and 30 wk of gestation. The primary outcome was supplemental calcium intake measured by pill counts 4 and 8 wk after recruitment. We carried out intention-to-treat analyses with the use of mixed-effect models, with regimen as the fixed effect and health care facilities as a random effect, by using a noninferiority margin of 125 mg Ca/d. Women in facilities assigned to the standard regimen consumed a mean of 1198 mg Ca/d, whereas those assigned to the low-dose regimen consumed 810 mg Ca/d. The difference in intake was 388 mg Ca/d (95% CI = 341, 434 mg Ca/d), exceeding the prespecified margin of 125 mg Ca/d. The overall adherence rate was 80% and did not differ between study arms. Contrary to our expectation, a simpler, lower-dose regimen led to significantly lower supplement intake than the regimen recommended by the WHO. Further studies are needed to precisely characterize the dose-response relation of calcium supplementation and preeclampsia risk and to examine cost effectiveness of lower and simpler regimens in program settings. This trial was registered at clinicaltrials.gov as NCT02238704.